Histochemical studies on the morphology of the Golgi apparatus and its relationship to catecholamine biosynthesis in the locus coeruleus of the rat.

Abstract

Detailed histochemical studies have been performed on the morphology of the Golgi apparatus (GA) by application of the thiamine pyrophosphatase (TPPase) method (Novikoff and Goldfischer, 1961) to the neurons of the locus coeruleus (LC) of normal and catecholamine biosynthesis inhibitors (fusaric acid and D, L-α-methyl-p-tyrosine methylester HCl) given adult healthy male Wistar strain rats. The neurons were classified into five categories on the basis of the morphology of the Golgi apparatus. The number of cells in individual categories was counted to evaluate the percentage of each category in the whole nucleus. The majority of cells belongs to Types II, III, and IV whose GA goes through cyclic activity, but the remaining neurons belong to Types I and V which may have a strong tendency to be different from the former in character. The latter neurons correspond formally with Types I and V of the rabbit LC, but they do not respond to the drugs administered. The rat LC is very similar to the dorsal vagal nucleus of the rabbit in regard to the dominant category. The present results indicate that the majority of the rat LC neurons may work vigorously and they may be motor neurons. Administration of the drugs caused reduction of TPPase activity, augmentation of disintegration and the budding-off process of the GA of Type IV, a decrease in the percentage of Type IV and an increase in that of Type II. Administration of 100 mg/kg fusaric acid caused maximal morphological change of the GA at the 90th minute; however, administration of 200 mg/kg fusaric acid showed more marked change of the GA, having two peaks and two valleys. The GA revealed much more intense reaction to D,L-α-methyl-p-tyrosine methylester HCl than to fusaric acid. The present results indicate that tyrosine hydroxylase may be the rate-limiting enzyme in the catecholamine biosynthesis. These noticeable changes of GA caused by administration of the drugs were completely restricted to the neurons of LC and the neurons of the mesencephalic nucleus of the trigeminal nerve did not show any morphological changes of the GA. These results strongly suggest that the GA of the rat LC neurons may have ability to synthesize catecholamine whereas the GA of the rat mesencephalic nucleus of the trigeminal nerve may be completely devoid of this ability and that the role of the GA may be different depending on the anatomical regions.